Question

Possible Duplicate:
The difference between the two functions? (“function x” vs “var x = function”)
JavaScript: var functionName = function() {} vs function functionName() {}

var test = function() {
    var a = 20;
    var b = 30;

    return a + b;
};

function Add() {
    var a = 20;
    var b = 30;

    return a + b;
}

What is the difference between these two functions? If I call add() or test() they both give me the same result. What exactly does the var do?

Answer 1

The function declaration syntax cannot be used within a block statement.

Legal:

function a() {
    function b() {

    }
}

Illegal:

function a() {
    if (c) {
        function b() {

        }
    }
}

You can do this though:

function a() {
    var b;
    if (c) {
        b = function() {

        };
    }
}

For the language nerds among us you’ll want to reference sections 12.1, 13.1, and 14 of the specification. You will find the following syntax descriptions.

12.1 Block

Syntax

Block :
    { StatementList_opt }

StatementList :
    Statement
    StatementList Statement

13 Function Definition

Syntax

FunctionDeclaration :

    function Identifier ( FormalParameterList_opt ) { FunctionBody }

FunctionExpression :

    function Identifier_opt ( FormalParameterList_opt ) { FunctionBody }

FormalParameterList :

    Identifier

    FormalParameterList , Identifier

FunctionBody :

    SourceElements

14 Program

Syntax

Program :

    SourceElements_opt

SourceElements :

    SourceElement

    SourceElements SourceElement

SourceElement :

    Statement

    FunctionDeclaration